The present invention relates to an illumination optical apparatus, an exposure apparatus, and a device manufacturing method. More particularly, the present invention relates to a reflection type illumination optical apparatus optimal for use in an exposure apparatus for manufacturing devices in a lithography process, such as a semiconductor element, imaging element, liquid crystal display element, and thin-film magnetic head.
In the prior art, in an exposure apparatus for manufacturing semiconductor elements and the like, a circuit pattern is formed on a mask (reticle) and thereafter projected and transferred onto a photosensitive substrate (e.g., wafer) through a projection optical system. Resist is applied to the photosensitive substrate. The resist is photosensitized by projection and exposure performed by a projection optical system. This obtains a resist pattern corresponding to a mask pattern. The resolution of the exposure apparatus is dependent on the wavelength of exposure light and the numerical aperture of the projection optical system.
In other words, the wavelength of the exposure light must be shortened and the numerical aperture of the projection optical system must be increased to improve the resolution of the exposure apparatus. It is generally difficult to increase the numerical aperture of the projection optical system to a level that is greater than or equal to a predetermined value from the viewpoint of optical design. Thus, the wavelength of the exposure light must be shortened. Accordingly, EUVL (Extreme Ultra-Violet Lithography) is gathering attention as a next-generation exposure method (exposure apparatus) for semiconductor patterning.
An EUVL exposure apparatus uses EUV (Extreme Ultra-Violet) light having a wavelength of about 5 to 20 nm, which is shorter that in the exposure method of the prior art that uses KrF excimer laser light having a wavelength of 248 nm or an ArF excimer laser light having a wavelength of 193 nm. When using EUV light as the exposure light, there is no usable light transmissive optical material. Thus, a reflection type optical integrator, a reflective mask (generally, reflective raw plate), and a reflection type projection optical system are used in the EUVL exposure apparatus (for example, refer to patent document 1).    [Patent document 1] U.S. Pat. No. 6,452,661